Based on the porous media theory and by taking into account the efects of the pore fuid viscidity, energy exchanges due to the additional thermal conduction and convection between solid and fuid phases, a mathematical...Based on the porous media theory and by taking into account the efects of the pore fuid viscidity, energy exchanges due to the additional thermal conduction and convection between solid and fuid phases, a mathematical model for the dynamic-thermo-hydro-mechanical coupling of a non-local thermal equilibrium fuid-saturated porous medium, in which the two constituents are assumed to be incompressible and immiscible, is established under the assumption of small de- formation of the solid phase, small velocity of the fuid phase and small temperature changes of the two constituents. The mathematical model of a local thermal equilibrium fuid-saturated porous medium can be obtained directly from the above one. Several Gurtin-type variational principles, especially Hu-Washizu type variational principles, for the initial boundary value problems of dy- namic and quasi-static responses are presented. It should be pointed out that these variational principles can be degenerated easily into the case of isothermal incompressible fuid-saturated elastic porous media, which have been discussed previously.展开更多
The reaction of C3H8＋O（^3p）→C3HT＋OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geo...The reaction of C3H8＋O（^3p）→C3HT＋OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Moller-Plesset perturbation method and the single-point energy is computed us- ing the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C3Hs＋O（^3p）→i- C3HT＋OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogenabstraction from propane involving reaction channel competitions is helpful for the understanding of propane combustion.展开更多
The seasonal variations of the intensity and location of the East Asian subtropical westerly jet （EAWJ） and the thermal mechanism are analyzed by using NCEP/NCAR monthly reanalysis data from 1961 to 2000. It is foun...The seasonal variations of the intensity and location of the East Asian subtropical westerly jet （EAWJ） and the thermal mechanism are analyzed by using NCEP/NCAR monthly reanalysis data from 1961 to 2000. It is found that the seasonal variation of the EAWJ center not only has significant meridional migration, but also shows the rapid zonal displacements during June-July. Moreover, there exists zonal inconsistency in the northward shift process of the EAWJ axis. Analysis on the thermal mechanism of the EAWJ seasonal variations indicates that the annual cycle of the EAWJ seasonal variation matches very well with the structure of the meridional difference of air temperature, suggesting that the EAWJ seasonal variation is closely related to the inhomogeneous heating due to the solar radiation and the land-sea thermal contrast. Through investigating the relation between the EAWJ and the heat transport, it is revealed that the EAWJ weakens and shifts northward during the warming period from wintertime to summertime, whereas the EAWJ intensifies and shifts southward during the cooling period from summertime to wintertime. The meridional difference of the horizontal heat advection transport is the main factor determining the meridional temperature difference. The meridional shift of the EAWJ follows the location of the maximum meridional gradient of the horizontal heat advection transport. During the period from April to October, the diabatic heating plays the leading role in the zonal displacement of the EAWJ center. The diabatic heating of the Tibetan Plateau to the mid-upper troposphere leads to the rapid zonal displacement of the EAWJ center during June-July.展开更多
This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencin...This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencing thermal cycles,it was found that both microstructures consisted of priorβ,grain boundaryα(GBα),and basketweave structures containingα+βlamellae.Thermal cycles realized the refinement ofαlaths,the coarsening of priorβgrains andβlaths,while the size and morphology of continuously distributed GBαremained unchanged.The residualβcontent was increased after thermal cycles.Compared with the heat-treated sample with nanoscale Ti2Cu formed,short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti2Cu formation.No formation of brittle Ti2Cu means that only grain refinement strengthening and solid-solution strengthening matter.The yield strength increased from 809.9 to 910.85 MPa(12.46%increase).Among them,the main contribution from solid solution strengthening(~51 MPa)was due to the elemental redistribution effect betweenαandβphases caused by thermal cycles through quantitative analysis.The ultimate tensile strength increased from 918.5 to 974.22 MPa(6.1%increase),while fracture elongation increased from 6.78 to 10.66%(57.23%increase).Grain refinement ofαlaths,the promotedα′martensite decomposition,decreased aspect ratio,decreased Schmid factor,and local misorientation change ofαlaths are the main factors in improved ductility.Additionally,although the fracture modes of the samples in the top and middle regions are both brittle-ductile mixed fracture mode,the thermal cycles still contributed to an improvement in tensile ductility.展开更多
基金Project supported by the National Natural Science Foundation of China(No.10272070)and the Development Foun-dation of the Education Commission of Shanghai,China.
文摘Based on the porous media theory and by taking into account the efects of the pore fuid viscidity, energy exchanges due to the additional thermal conduction and convection between solid and fuid phases, a mathematical model for the dynamic-thermo-hydro-mechanical coupling of a non-local thermal equilibrium fuid-saturated porous medium, in which the two constituents are assumed to be incompressible and immiscible, is established under the assumption of small de- formation of the solid phase, small velocity of the fuid phase and small temperature changes of the two constituents. The mathematical model of a local thermal equilibrium fuid-saturated porous medium can be obtained directly from the above one. Several Gurtin-type variational principles, especially Hu-Washizu type variational principles, for the initial boundary value problems of dy- namic and quasi-static responses are presented. It should be pointed out that these variational principles can be degenerated easily into the case of isothermal incompressible fuid-saturated elastic porous media, which have been discussed previously.
文摘The reaction of C3H8＋O（^3p）→C3HT＋OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Moller-Plesset perturbation method and the single-point energy is computed us- ing the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C3Hs＋O（^3p）→i- C3HT＋OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogenabstraction from propane involving reaction channel competitions is helpful for the understanding of propane combustion.
基金the National Natural Science Foundation of China under Grant Nos. 40675041, 40333026, and 40672210.
文摘The seasonal variations of the intensity and location of the East Asian subtropical westerly jet （EAWJ） and the thermal mechanism are analyzed by using NCEP/NCAR monthly reanalysis data from 1961 to 2000. It is found that the seasonal variation of the EAWJ center not only has significant meridional migration, but also shows the rapid zonal displacements during June-July. Moreover, there exists zonal inconsistency in the northward shift process of the EAWJ axis. Analysis on the thermal mechanism of the EAWJ seasonal variations indicates that the annual cycle of the EAWJ seasonal variation matches very well with the structure of the meridional difference of air temperature, suggesting that the EAWJ seasonal variation is closely related to the inhomogeneous heating due to the solar radiation and the land-sea thermal contrast. Through investigating the relation between the EAWJ and the heat transport, it is revealed that the EAWJ weakens and shifts northward during the warming period from wintertime to summertime, whereas the EAWJ intensifies and shifts southward during the cooling period from summertime to wintertime. The meridional difference of the horizontal heat advection transport is the main factor determining the meridional temperature difference. The meridional shift of the EAWJ follows the location of the maximum meridional gradient of the horizontal heat advection transport. During the period from April to October, the diabatic heating plays the leading role in the zonal displacement of the EAWJ center. The diabatic heating of the Tibetan Plateau to the mid-upper troposphere leads to the rapid zonal displacement of the EAWJ center during June-July.
基金sponsored by the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact 2021ZX52002222019the Natural Science Foundation of China(NSFC No.U2141216)the Chongqing Technology Innovation and Application Special Program.
文摘This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencing thermal cycles,it was found that both microstructures consisted of priorβ,grain boundaryα(GBα),and basketweave structures containingα+βlamellae.Thermal cycles realized the refinement ofαlaths,the coarsening of priorβgrains andβlaths,while the size and morphology of continuously distributed GBαremained unchanged.The residualβcontent was increased after thermal cycles.Compared with the heat-treated sample with nanoscale Ti2Cu formed,short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti2Cu formation.No formation of brittle Ti2Cu means that only grain refinement strengthening and solid-solution strengthening matter.The yield strength increased from 809.9 to 910.85 MPa(12.46%increase).Among them,the main contribution from solid solution strengthening(~51 MPa)was due to the elemental redistribution effect betweenαandβphases caused by thermal cycles through quantitative analysis.The ultimate tensile strength increased from 918.5 to 974.22 MPa(6.1%increase),while fracture elongation increased from 6.78 to 10.66%(57.23%increase).Grain refinement ofαlaths,the promotedα′martensite decomposition,decreased aspect ratio,decreased Schmid factor,and local misorientation change ofαlaths are the main factors in improved ductility.Additionally,although the fracture modes of the samples in the top and middle regions are both brittle-ductile mixed fracture mode,the thermal cycles still contributed to an improvement in tensile ductility.
